This invention relates to fuses and more particularly to a fuse configuration adapted to interrupt high currents and particularly adapted for use with large value AC or DC currents.
As is well known, there are many examples of fuses in the prior art. A fuse is basically a device which is normally applied in series with current to be monitored and if the current exceeds a predetermined value, the fuse will interrupt the current and hence, remove power from the circuit or system being monitored by the fuse. As indicated, there are many examples of fuses of various configurations which will serve to operate in conjunction with both AC or DC currents.
Basically, the problem of incorporating a fuse in a DC circuit exhibits many different requirements as compared to current interruption in an AC circuit. In this respect, many fuse manufacturers have two different types of fuses; one of which is intended for AC operation and the other intended for DC operation. As such, DC fuses in the prior art require a plurality of elements as fuse links which are connected in parallel and such fuses perform fairly well for major overload currents and so on. An AC fuse may be employed in a DC circuit, but one has to derate the fuse by as much as fifty percent.
In any event, one experiences substantial problems in interrupting high level DC currents. Amoung these problems are circuit interuption at moderate values of overload, creating gas pressures during arcing and the buildup of various deleterious substances during fuse operation, which substances tend to effect the overall performance of fuse operation. Such fuses must operate at small overload currents which may last for a prolonged period as well as operating with a high overload current which may exist for a shorter interval. The fuse must be compatible with all types of circuit loads such as inductive loads which may produce or provide excessive startup currents.
Many fuses in the prior art utilize a ribbon-type fuse link in conjunction with a rod upon which a portion of the fuse link is wrapped or directed. An example of a typical DC fuse found in the prior art may be had by referring to U.S. Pat. No. 3,935,553, entitled CARTRIDGE FUSE FOR DC CIRCUITS by Kozacka et al issued on Jan. 27, 1976.
Essentially, the fuse as above indicated has been employed for many years and various developments have been made in regard to superior materials and alternate configurations. For example, U.S. Pat. No. 3,940,728 entitled ALLOY FOR A HIGH TEMPERATURE FUSE issued on Feb. 24, 1976 to Komatsu et al depicts an alloy consisting of copper and aluminum and an additional metal such as nickel, maganese and iron and exhibits temperature operation within a range of 1,000.degree. to 1,100.degree. C. Such fuses are employed as temperature fuses but certain of these alloys may be used to interrupt electrical currents.
A number of patents such as U.S. Pat. No. 3,662,310 and U.S. Pat. No. 4,101,860 depict electrical fuses which operate in conjunction with a suitable filler such as quartz sand or employ housings fabricated from an inorganic ceramic material such as aluminum oxide, beryllium oxide, boron nitride, steatite, sullite and cordierite. The fuses which employ these housings also use a heat insulating arc quenching material such as quartz, sand or calcium sulphate. These materials serve to absorb heat under various temperature conditions and hence, by selection of the housing and the filler material as disclosed in the prior art patents, different operating characteristics can be provided for the fuse.
It is, of course, understood that a major component of any fuse is the fuse link which, as indicated by the prior art, comprises many different configurations; some of which are extremely difficult to fabricate and therefore are extremely expensive. Examples of certain prior art fuse links are depicted in U.S. Pat. No. 3,471,818 entitled UNITARY FULL RANGE CURRENT CLEARING FUSIBLE ELEMENT and U.S. Pat. No. 3,689,995 entitled ELECTRIC FUSES. Still other patents show alternate configurations for high current fuse operation employing various fuse link configurations as U.S. Pat. No. 2,376,809 entitled CIRCUIT INTERRUPTER.
It is therefore extremely desirable to provide a single fuse for both AC and DC operation; which fuse possesses the same current ratings for both modes of operation, while exhibiting reliable operation under DC conditions as well as AC conditions.
In view of the above, it is an object of this invention to provide reliable and improved fuse apparatus which is capable of operating to interrupt high level AC or DC currents and will respond to both large overloads and small overloads. The apparatus employed is easy to fabricate in employing conventional materials in a unique arrangement.